Effect of Arsenic Compounds 



57 



arsenate has little or no action, though it is just possible that the rather 

 irregular curves indicate a very slight depression below the normal 

 throughout. 



(b) Toxic effect of arsenic compounds in sand cultures. 



Comparatively few tests seem to have been made as to the action 

 of arsenical solutions in sand cultures. Stoklasa (1898) repeated his 

 water culture work, using sand as a medium, and found analogous results 

 by the two methods, i.e. that arsenites are far more toxic than arsenates, 

 and also that the degree of toxicity of a salt varies with the plant to 



Fig. 14. Curve showing the mean value of the dry weights of ten series of pea plants 

 grown in the presence of sodium arsenite and nutrient salts. (June 27th Aug. 10th, 

 1911.) 



which it is applied, as was shown by the fact that different plants lived 

 for varying times when treated with similar strengths of solution. 



(c) Toxic effect of arsenic when applied to soil cultures. 



Daubeny (1862) watered barley plants with a solution of arsenious 

 acid, 1 ounce in 10 gallons, five times in succession, and found that the 

 crop arrived at maturity about a fortnight earlier than the untreated 

 part of the crop, though the amount harvested was rather less. With 

 turnips four waterings had no effect upon the time of maturity, but 

 again the crop was slightly decreased. The analyses made indicated 

 that no arsenic was taken into the tissues, but that it merely adhered 

 to the external surfaces. 



